1. Field of the Invention
The present invention relates generally to the field of aerodynamics and, more specifically, to a structure for reducing drag and increasing lift on aerodynamic or on hydrodynamic surfaces with sharp or moderately blunt trailing edges.
2. Description of the Related Art
Typically, aerodynamic and/or hydrodynamic surfaces have sharp or moderately blunt trailing edges from which the wake is shed. The strength, distribution and direction of wake turbulence separation, and vorticity, and the location of the beginning of the wake are sources of increased drag and reduced lift, both of which are highly undesirable.
Generally, trailing edge devices which have been used to increase lift either have no effect on drag or have a negative effect on drag, and thus, trade-offs between lift and drag are normally expected. No trailing edge devices are currently known in the art which passively provide both drag reduction and lift improvement for with sharp or moderately blunt trailing edges. One attampt to reduce the base drag of wings with very thick, blunt trailing edges wherein the trailing edge has a thickness of more than five to ten percent of the wing chord has been to provide the trailing edge with span-wise indentations or splitter blades. In another device, a rippled trailing edge has been used to increase maximum lift by delaying the onset of massive boundary layer separation over very thick airfoils where the wing thickness is 20% of the wing chord and where low Reynolds numbers are experienced (about 100,000 based on the wing chord and the freestream velocity). However, neither approach simultaneously increased lift and reduced drag.
Another trailing edge device is known as the Gurney flap, and is illustrated generically on the trailing edge of an airfoil illustrated schematically in FIG. 1. The Gurney flap mounted perpendicularly to the chord, has been used to increase maximum lifting capability of airfoils. However, the two dimensional span-wise invariant Gurney flap does not modify the trailing-edge flow in a spanwise-periodic fashion, and thus does not alter the three-dimensional vorticity field in the region near and immediately behind the trailing edge. Also, the Gurney flap does not reduce drag for a given amount of lift.
None of the above-described devices have been proven to improve lift while decreasing drag associated with aerodynamically sharp trailing edges or trailing edges with moderate bluntness. Although the rippled trailing edge and the Gurney flap produced an increase in maximum lift, it concomitantly produced an undesirable drag penalty at cruise and climb conditions. Thus, a continuing need exists for devices which can produce increased lift while not increasing drag.